[dm-devel] [PATCH] blk-settings: make sure that max_sectors is aligned on "logical_block_size" boundary.

[Sweet Tea Dorminy]

Greetings;

Might I suggest using SECTOR_SIZE instead of 512? Or, perhaps, >>
SECTOR_SHIFT instead of / 512.

I don't understand the three conditionals. I believe max_sectors is
supposed to be <= min(max_dev_sectors, max_hw_sectors), but I don't
understand why max_sectors being small should adjust max_hw_sectors and
max_dev_sectors. Are the conditions perhaps supposed to be different,
adjusting each max_*sectors up to at least PAGE_SIZE / SECTOR_SIZE?
Perhaps, like e.g. blk_queue_max_hw_sectors(), the conditionals should log
if they are adjusting max_*sectors up to the minimum.

Thanks!

John Dorminy

On Thu, Nov 19, 2020 at 3:37 PM Mikulas Patocka <mpatocka at redhat.com> wrote:

> We get these I/O errors when we run md-raid1 on the top of dm-integrity on
> the top of ramdisk:
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8048, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8147, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8246, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8345, 0xbb
>
> The ramdisk device has logical_block_size 512 and max_sectors 255. The
> dm-integrity device uses logical_block_size 4096 and it doesn't affect the
> "max_sectors" value - thus, it inherits 255 from the ramdisk. So, we have
> a device with max_sectors not aligned on logical_block_size.
>
> The md-raid device sees that the underlying leg has max_sectors 255 and it
> will split the bios on 255-sector boundary, making the bios unaligned on
> logical_block_size.
>
> In order to fix the bug, we round down max_sectors to logical_block_size.
>
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> Cc: stable at vger.kernel.org
>
> ---
>  block/blk-settings.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> Index: linux-2.6/block/blk-settings.c
> ===================================================================
> --- linux-2.6.orig/block/blk-settings.c 2020-10-29 12:20:46.000000000 +0100
> +++ linux-2.6/block/blk-settings.c      2020-11-19 21:20:18.000000000 +0100
> @@ -591,6 +591,16 @@ int blk_stack_limits(struct queue_limits
>                 ret = -1;
>         }
>
> +       t->max_sectors = round_down(t->max_sectors, t->logical_block_size
> / 512);
> +       if (t->max_sectors < PAGE_SIZE / 512)
> +               t->max_sectors = PAGE_SIZE / 512;
> +       t->max_hw_sectors = round_down(t->max_hw_sectors,
> t->logical_block_size / 512);
> +       if (t->max_sectors < PAGE_SIZE / 512)
> +               t->max_hw_sectors = PAGE_SIZE / 512;
> +       t->max_dev_sectors = round_down(t->max_dev_sectors,
> t->logical_block_size / 512);
> +       if (t->max_sectors < PAGE_SIZE / 512)
> +               t->max_dev_sectors = PAGE_SIZE / 512;
> +
>         /* Discard alignment and granularity */
>         if (b->discard_granularity) {
>                 alignment = queue_limit_discard_alignment(b, start);
>
> --
> dm-devel mailing list
> dm-devel at redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>
>
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